The invention relates to a ribbed construction assembled from sheet metal bands for improved heat transfer suitably built into the pipes of heat exchangers.
The ribbed construction according to the invention improves the heat transfer primarily by slowing down the velocity of the medium flowing through the central part of the pipe; furthermore it improves the temperature distribution of the medium in the cross section of the pipe by metallic conduction and mixing. Although the ribs in the pipe are easily movable, a significant portion of the tooth ends are in loose contact with the inner wall of the pipe, thereby improving the heat transfer.
It is well-known that the heat transfer between the media of high viscosity and the pipes through which the media flows is very poor due to ineffective heat conduction. This is caused by the so-called laminar flow of these media in the pipe, i.e. there is no, or hardly any, flow in the immediate vicinity of the wall, while moving away from the pipe wall towards the center of the pipe, the flow velocity increases. Since there is virtually no mixing over the cross section, the heat can only pass between the large quantity of liquid flowing in the center of the pipe cross section and the pipe wall, if it passes through the layers near the pipe wall. These layers represent genuine thermal insulation on the inner pipe wall in the case of a poor heat conducting medium, and thus they considerably inhibit the heat transfer.
In the techniques of the state of the art, in order to improve the heat transfer conditions, the internal surface of the pipe is provided with ribs, whereby the heat transfer surface is increased, these ribs extend partially into the center of the pipe cross section, there exerting a direct cooling effect.
The internal ribs fitted in the pipe are known as internal rib solutions. These may be formed from the material of the pipe itself, or welded to the inner surface of the pipe. Furthermore the internal ribs which are removable from the pipe and fixed therein only by friction, are also known, being in contact with the pipe wall, thereby ensuring metallic contact between the rib and pipe.
The first solution completely fulfills the goal of the rib's cooling effect which is excellent, since even in case of welding, the heat is transmitted to the pipe wall through metallic contact. However, the production of such ribbed pipe is fairly costly, making the cleaning of the pipe interior difficult or even impossible.
The second solution facilitates the cleaning, because the ribs are removable from the pipe, but in the interest of removability, the ribs can not have a tight fit with the inner pipe wall, thus the metallic contact between the ribs and the pipe deteriorates, especially after several insertions and removals.